Passivation to reduce the surface recombination of minority carriers is of key importance for improving photovoltaic efficiency, especially for thin devices. High quality electronic passivation is achieved for surface recombination velocities (SRV)≦10 cm s-1. (FIG. 1) Chemical vapor deposition (CVD) is currently used in industry to deposit 65-150 nm thick SiNx, which also acts as an anti-reflective coating (ARC). The high temperature of the SiNx degrades the quality of the bulk Si and raises operational costs.
By contrast, low temperature processing retains organic functionalities, enabling the fabrication of hybrid or multi-functional devices. Protocols for organic passivation typically start with chemical etching of the native silicon oxide to obtain H-terminated Si surfaces. The Si—H bonds are subsequently activated by various solution methods. Most organic passivations rely on monolayer coverage rather than on producing layers with nano-scale thickness, as is the case for SiNx passivation. A two-step chlorination/alkylation scheme produces low air-stable SRV among organic passivations; however, the time-consuming process and stringent limitations on ambient water and oxygen contents have hindered its industrial application. Ethanol-iodine (E-I) passivation produces SRV ˜10 cm s-1, but this value increases to 10^3 cm s-1 within minutes in air. E-I still serves as a good reference for high-quality passivation due to its ease of preparation.